Holographic display apparatus and holographic display method

ABSTRACT

A holographic display apparatus includes a spatial light modulator configured to generate hologram patterns to modulate light; an illuminator configured to emit the light to the spatial light modulator; and a controller configured to control operations of the spatial light modulator and the illuminator, the spatial light modulator being configured to generate, from among the hologram patterns, a first hologram pattern and a second hologram pattern according to the control operations of the controller, the first hologram pattern and the second hologram pattern being configured to form a first hologram image and a second hologram image having different viewpoints, and the controller being configured to set a first phase modulation value of the first hologram pattern and a second phase modulation value of the second hologram pattern to be different from each other such that hologram images having different viewpoints are formed.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 14/881,671,filed Oct. 13, 2015, which claims priority to Korean Patent ApplicationNo. 10-2014-0136959, filed on Oct. 10, 2014, and Korean PatentApplication No. 10-2015-0127036, filed on Sep. 8, 2015 filed in theKorean Intellectual Property Office, the disclosure of which isincorporated herein in its entirety by reference.

BACKGROUND 1. Field

The exemplary embodiments disclosed in the present disclosure relate toa holographic display apparatus and a holographic display method, andmore particularly, to a holographic display apparatus and a holographicdisplay method capable of preventing binocular crosstalk while providinghologram images having different viewpoints to the left and right eyesof an observer.

2. Description of the Related Art

As methods of realizing 3D images, methods which use glasses (alsoreferred to as “glasses methods”) and methods which do not use glasses(also referred to as “non-glasses methods”) are widely used. Examples ofthe glasses methods include deflected glasses methods and shutterglasses methods, and examples of the non-glasses methods includelenticular methods and parallax barrier methods. Such methods usebinocular parallax and are limited in increasing the number ofviewpoints. In addition to this, these methods make viewers feel tireddue to the difference between the depth of images, which the brainperceives, and the focus of the eyes.

Recently, holographic display methods, which are 3D image displaymethods capable of making the depth, which the brain perceives,consistent with the focus of the eyes and providing full parallax, havebeen gradually put to practical use. A holographic display techniqueuses a principle that once reference light is irradiated onto a hologrampattern having recorded thereon an interference pattern obtained byinterference between object light reflected from an original object andthe reference light, the reference light is diffracted, and an image ofthe original object is reproduced. A currently commercializedholographic display technique provides a computer-generated hologram(CGH), rather than the hologram pattern obtained by directly exposingthe original object to light, as an electric signal to a spatial lightmodulator. The spatial light modulator forms the hologram pattern anddiffracts incident light according to the input CGH signal, therebygenerating a 3D image.

However, a very high resolution spatial light modulator and a very largeamount of data processing are required to implement a perfectholographic display technique. Recently, to reduce the amount of dataprocessing required to be performed while still achieving a sufficientresolution, a binocular hologram technique of providing hologram imagesto only a viewing zone corresponding to both eyes of the observer hasbeen proposed. For example, a hologram image having a viewpointcorresponding to a left-eye viewing zone of the observer and a hologramimage having a viewpoint corresponding to a right-eye viewing zone ofthe observer are generated and provided to the left and right eyes ofthe observer, respectively. In this case, no hologram image for otherviewpoints is generated, and thus, a data processing amount may begreatly reduced, and a currently commercialized display apparatus maysatisfy a resolution condition of the spatial light modulator.

SUMMARY

According to an aspect of an exemplary embodiment, there is provided aholographic display apparatus including: a spatial light modulatorconfigured to generate hologram patterns to modulate light; anilluminator configured to emit the light to the spatial light modulator;and a controller configured to control operations of the spatial lightmodulator and the illuminator, wherein the spatial light modulator isconfigured to generate, from among the hologram patterns, a firsthologram pattern and a second hologram pattern according to the controloperations of the controller, the first hologram pattern and the secondhologram pattern being configured to form a first hologram image and asecond hologram image having different viewpoints, and wherein thecontroller is configured to set a first phase modulation value of thefirst hologram pattern and a second phase modulation value of the secondhologram pattern to be different from each other such that hologramimages having different viewpoints formed by the first hologram patternand the second hologram pattern are formed on different spatiallocations.

The controller may be configured to control the spatial light modulatorto alternately scan the first hologram pattern and the second hologrampattern in a progressive scanning way in order to alternately form thefirst hologram image and the second hologram image in a time divisionway.

The spatial light modulator may be configured to display the firsthologram pattern on a first frame, the second hologram pattern on asecond frame that is subsequent to the first frame, a part of the firsthologram pattern on a partial area of the spatial light modulator, and apart of the second hologram pattern on a remaining partial area of thespatial light modulator during a transition period between the firstframe and the second frame.

The controller may be configured to set the first phase modulation valuesuch that the first hologram image modulated and formed by the firsthologram pattern is transmitted to a first viewing zone and to set thesecond phase modulation value such that the second hologram imagemodulated and formed by the second hologram pattern is transmitted to asecond viewing zone different from the first viewing zone during thetransition period.

The controller may be configured to control the spatial light modulatorto overlap and display the first hologram pattern and the secondhologram pattern on one frame.

The controller may be configured to set the first phase modulation valuesuch that the first hologram image formed by the first hologram patternamong the overlapped first hologram pattern and second hologram patternis transmitted to a first viewing zone and set the second phasemodulation value such that the second hologram image modulated andformed by the second hologram pattern is transmitted to a second viewingzone different from the first viewing zone.

The illuminator may include one light source configured to emit light.

The controller may be configured to set the first phase modulation valuesuch that the first hologram image formed by modulating light emitted bythe light source by using the first hologram pattern is incident to afirst viewing zone, and to set the second phase modulation value suchthat the second hologram image formed by modulating the light emitted bythe light source by using the second hologram pattern is incident to asecond viewing zone different from the first viewing zone.

The illuminator may include a first light source configured to emitlight for forming the first hologram image and a second light sourceconfigured to emit light for forming the second hologram image.

The controller may be configured to set the first phase modulation valuesuch that the first hologram image formed by modulating light emitted bythe first light source by using a first hologram pattern is incident toa first viewing zone, and a third hologram image formed by modulatinglight emitted by the second light source by using the first hologrampattern is incident to a location beyond a second viewing zone.

The controller may be configured to set the second phase modulationvalue such that the second hologram image formed by modulating the lightemitted by the second light source by using a second hologram pattern isincident to the second viewing zone, and a fourth hologram image formedby modulating the light emitted by the first light source by using thesecond hologram pattern is incident to a location beyond the firstviewing zone.

The holographic display apparatus may further include an eye trackerconfigured to track a pupil location of an observer observing the firsthologram image, the second hologram image, the third hologram image andthe fourth hologram image, wherein the controller may be configured tochange the first phase modulation value and the second phase modulationvalue such that a location difference between the first hologram imageand the fourth hologram image and a location difference between thesecond hologram image and the third hologram image are maintained to begreater than sizes of the pupils of the observer in response to a pupillocation change of the observer.

The first light source and the second light source may be configured tosimultaneously provide light to the spatial light modulator.

The first hologram pattern may be represented as a product of hologramdata of the first hologram image multiplied with the first phasemodulation value, and the second hologram pattern may be represented asa product of hologram data of the second hologram image multiplied withthe second phase modulation value.

According to an aspect of another exemplary embodiment, there isprovided a holographic display apparatus including: a spatial lightmodulator configured to generate hologram patterns to modulate incidentlight; an illuminator configured to emit light to the spatial lightmodulator; and a controller configured to control the spatial lightmodulator and the illuminator, wherein the spatial light modulator isconfigured to simultaneously generate, from among the hologram patterns,a first hologram pattern that modulates the incident light as a firsthologram image and a second hologram pattern that modulates the incidentlight as a second hologram image, and wherein the controller isconfigured to set a first phase modulation value of the first hologrampattern and a second phase modulation value of the second hologrampattern to be different from each other such that a location differencebetween the first hologram image and the second hologram image ismaintained to be greater than sizes of pupils of an observer observingthe first hologram image and the second hologram image.

The illuminator may include one light source configured to emit light.

The controller may be configured to set the first phase modulation valuesuch that the first hologram image formed by modulating the lightemitted by the light source by using the first hologram pattern isincident to a first viewing zone, and to set the second phase modulationvalue such that the second hologram image formed by modulating the lightemitted by the light source by using the second hologram pattern isincident to a second viewing zone different from the first viewing zone.

The illuminator may include a first light source configured to emitlight for forming the first hologram image and a second light sourceconfigured to emit light for forming the second hologram image.

The controller may be configured to set the first phase modulation valuesuch that the first hologram image formed by modulating the lightemitted by the first light source by using a first hologram pattern isincident to a first viewing zone, and a third hologram image formed bymodulating the light emitted by the second light source by using thefirst hologram pattern is incident to a location beyond a second viewingzone.

The controller may be configured to set the second phase modulationvalue such that the second hologram image formed by modulating the lightemitted by the second light source unit by using a second hologrampattern is incident to the second viewing zone, and a fourth hologramimage formed by modulating the light emitted by the first light sourceby using the second hologram pattern is incident to a location beyondthe first viewing zone.

The controller may be configured to set the first phase modulation valueand the second phase modulation value such that a location differencebetween the first hologram image and the fourth hologram image and alocation difference between the second hologram image and the thirdhologram image are maintained to be greater than sizes of the pupils ofan observer.

According to an aspect of another exemplary embodiment, there isprovided a holographic display method comprising: emitting light to aspatial light modulator; and simultaneously forming, by the spatiallight modulator, a first hologram pattern that modulates the light as afirst hologram image and a second hologram pattern that modulates thelight as a second hologram image, wherein the simultaneously formingcomprises setting a first phase modulation value of the first hologrampattern and a second phase modulation value of the second hologrampattern to be different from each other such that a location differencebetween the first hologram image and the second hologram image ismaintained to be greater than sizes of pupils of an observer observingthe first hologram image and the second hologram image.

The emitting of the light to the spatial light modulator may includeemitting the light using one light source, and the simultaneouslyforming may include setting the first phase modulation value such thatthe first hologram image formed by modulating the light emitted by thelight source by using the first hologram pattern is incident to a firstviewing zone, and setting the second phase modulation value such thatthe second hologram image formed by modulating the light emitted by thelight source by using the second hologram pattern is incident to asecond viewing zone different from the first viewing zone.

The emitting of the light to the spatial light modulator may includeemitting the light using a first light source which emits light forforming the first hologram image and a second light source which emitslight for forming the second hologram image, and the simultaneouslyforming may include setting the first phase modulation value such thatthe first hologram image formed by modulating the light emitted by thefirst light source by using a first hologram pattern is incident to afirst viewing zone, and a third hologram image formed by modulating thelight emitted by the second light source by using the first hologrampattern is incident to a location beyond a second viewing zone.

The simultaneously forming may include setting the second phasemodulation value such that the second hologram image formed bymodulating the light emitted by the second light source by using asecond hologram pattern is incident to the second viewing zone, and afourth hologram image formed by modulating the light emitted by thefirst light source unit by using the second hologram pattern is incidentto a location beyond the first viewing zone.

The simultaneously forming may include setting the first phasemodulation value and the second phase modulation value such that alocation difference between the first hologram image and the fourthhologram image and a location difference between the second hologramimage and the third hologram image are maintained to be greater thansizes of the pupils of an observer.

The first hologram pattern may be represented as a product of hologramdata of the first hologram image multiplied with the first phasemodulation value, and the second hologram pattern may be represented asa product of hologram data of the second hologram image m the secondphase modulation value.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the exemplary embodiments,taken in conjunction with the accompanying drawings in which:

FIG. 1 is a conceptual diagram schematically showing a structure of aholographic display apparatus according to an exemplary embodiment;

FIGS. 2A and 2B are exemplary diagrams of operations of the holographicdisplay apparatus providing hologram images having different viewpointsto the left and right eyes of an observer in a time divisional way;

FIG. 3 is an exemplary diagram of a process in which a spatial lightmodulator scans hologram patterns in a progressive scan way whenproviding hologram images in a time divisional way;

FIG. 4 is an exemplary diagram of a holographic display apparatus thatprovides hologram images of different viewpoints to left and right-eyeviewing zones of an observer without binocular crosstalk during atransition period between frames;

FIG. 5 is an exemplary diagram of a holographic display apparatus thatsimultaneously provides hologram images of different viewpoints to leftand right-eye viewing zones of an observer;

FIG. 6 is an exemplary diagram for describing a process in which aspatial light modulator scans hologram patterns when simultaneouslyproviding hologram images of different viewpoints to left and right-eyeviewing zones of an observer;

FIG. 7 is a conceptual diagram schematically showing a structure of aholographic display apparatus according to another exemplary embodiment;

FIGS. 8A and 8B are exemplary diagrams of operations of the holographicdisplay apparatus of FIG. 7 providing hologram images having differentviewpoints to left and right-eye viewing zones of an observer in a timedivisional way;

FIG. 9A is an exemplary diagram of an operation of a holographic displayapparatus generating a hologram image in a right-eye viewing zone of anobserver when a second light source unit of the holographic displayapparatus of FIG. 7 provides light to a spatial light modulator;

FIG. 9B is an exemplary diagram of an operation of a holographic displayapparatus generating a hologram image in a left-eye viewing zone of anobserver when a first light source unit of the holographic displayapparatus of FIG. 7 provides light to a spatial light modulator;

FIG. 10 is an exemplary diagram of a status in which hologram imageshaving different viewpoints are provided to left and right-eye viewingzones of an observer without binocular crosstalk;

FIG. 11 is an exemplary diagram of an operation of a holographic displayapparatus generating hologram images in left and right-eye viewing zonesof an observer when first and second light source units providereference light to a spatial light modulator;

FIG. 12 is an exemplary timing diagram of a process of operating anillumination unit and a spatial light modulator in the operation of theholographic display apparatus of FIG. 11;

FIGS. 13A, 13B, 14A, and 14B are actually formed hologram images inwhich no crosstalk occurs;

FIG. 15 is an exemplary diagram of an operation of a holographic displayapparatus simultaneously providing hologram images having differentviewpoints in a left-eye viewing zone and a right-eye viewing zone of anobserver; and

FIG. 16 is an exemplary timing diagram of a process of operating anillumination unit and a spatial light modulator in the operation of theholographic display apparatus of FIG. 15.

DETAILED DESCRIPTION

Hereinafter, with reference to the accompanying drawings, a holographicdisplay apparatus and method will be described in detail. Like referencenumerals refer to like elements throughout, and in the drawings, sizesof elements may be exaggerated for clarity and convenience ofexplanation. The exemplary embodiments described below are merelyexemplary, and various modifications may be possible from the exemplaryembodiments. In a layer structure described below, an expression “above”or “on” may include not only “immediately on in a contact manner” butalso “on in a non-contact manner”. As used herein, the term “and/or”includes any and all combinations of one or more of the associatedlisted items.

FIG. 1 is a conceptual diagram schematically showing a structure of aholographic display apparatus 100 according to an exemplary embodiment.The holographic display apparatus 100 according to an exemplaryembodiment may include a spatial light modulator 120 forming a hologrampattern for modulating incident light, an illumination unit 110 (e.g.,illuminator) providing the incident light to the spatial light modulator120, and a control unit 130 (e.g., controller) controlling operations ofthe spatial light modulator 120 and the illumination unit 110. Theholographic display apparatus 100 may further include an eye trackingunit 150 (e.g., eye tracker) tracking a pupil location of an observer.

The illumination unit 110 may include one light source unit providingcollimated light in the spatial light modulator 120. Although not shown,the illumination unit 110 may further include a collimating opticalelement for collimating light. Alternatively, the illumination unit 110may use a light source emitting collimated light. The light emitted fromthe illumination unit 110 may be perpendicularly incident to the spatiallight modulator 120. To provide light having a high spatial coherence,the illumination unit 110 may include a laser as a light source.However, if light has a certain degree of spatial coherence, since theincident light may be sufficiently diffracted and modulated by thespatial light modulator 120, a light-emitting diode (LED) may be used asthe light source. In addition to the LED, any other light sources may beused as long as light having spatial coherence is emitted. Although notshown in detail, one light source unit of the illumination unit 110 maybe configured as an array of a plurality of light sources.

The spatial light modulator 120 may form a hologram pattern fordiffracting and modulating the incident light, according to a hologramsignal provided by the control unit 130. The light spatial modulator 120may use any one of a phase modulator for performing phase modulation, anamplitude modulator for performing amplitude modulation, and a complexmodulator performing both phase modulation and amplitude modulation.Although the spatial light modulator 120 of FIG. 1 is a transmissivespatial light modulator, a reflective spatial light modulator may alsobe used. The transmissive light spatial modulator may use, for example,a semiconductor modulator based on a compound semiconductor such asGaAs, or a liquid crystal device (LCD). The reflective spatial lightmodulator may use, for example, a digital micromirror device (DMD), aliquid crystal on silicon (LCoS), or a semiconductor modulator.

The control unit 130 may be configured to generate the hologram signalaccording to the hologram image that is to be provided to the observer,provide the hologram signal to the spatial light modulator 120, andcontrol an operation of the illumination unit 110. For example, thecontrol unit 130 may turn on or off the illumination unit 110. Thecontrol unit 130 may be implemented by using software or a semiconductorchip functioning as the software.

The eye tracking unit 150 may obtain an image of the observer through acamera, detect the pupils of the observer from the image, and analyzethe locations of the pupils. The eye tracking unit 150 may track a pupillocation change of the observer and provide the pupil location change tothe control unit 130.

The holographic display apparatus 100 having the structure describedabove may provide hologram images having different viewpoints to theleft eye EL and the right eye ER of the observer in a binocularholographic way. For example, the holographic display apparatus 100 mayprovide a first hologram image to a left eye EL viewing zone of theobserver and a second hologram image to a right eye ER viewing zonehaving a different viewpoint from that of the first hologram image whiledetermining locations of the left eye EL and the right eye ER of theobserver by using the eye tracking unit 150. To this end, the spatiallight modulator 120 may form a first hologram pattern for the firsthologram image and a second hologram pattern for the second hologramimage according to control of the control unit 130.

For example, FIGS. 2A and 2B are exemplary diagrams of operations of theholographic display apparatus 100 providing hologram images havingdifferent viewpoints to the left eye EL and the right eye ER of anobserver in a time divisional way.

Referring to FIG. 2A, the spatial light modulator 120 forms a firsthologram pattern PL according to a hologram signal provided by thecontrol unit 130 at a first time. The illumination unit 110 provideslight to the spatial light modulator 120. Then, light incident to thespatial light modulator 120 is diffracted and modulated by the firsthologram pattern PL, and thus, object light may be reproduced. Theobject light may be projected to a left eye EL viewing zone of theobserver, and thus, a first hologram image L may be formed. Thus, thefirst hologram image L may be seen by the left eye EL of the observer atthe first time.

To form the first hologram image L in the left eye EL viewing zone ofthe observer by exactly projecting the object light to the left eye ELviewing zone of the observer, a phase modulation transfer function maybe used according to Equation 1 below.

t _(A)(x,y)=exp[jk(x cos θ+y sin θ)tan α]  [Equation 1]

In Equation 1 above, it is assumed that the spatial light modulator 120is placed on an x-y plane. α denotes an angle between the incident lightand the object light. θ denotes an orientation angle of the object lighton the x-y plane.

The first hologram pattern PL may be expressed as a multiplication HL×tLof a phase modulation value tL of the phase modulation transfer functionof Equation 1 above and hologram data HL of the first hologram image L.The hologram data may be previously generated according to an image thatis to be reproduced, for example, computer generated hologram (CGH)data. That is, the hologram data may include information regarding theimage that is to be reproduced, and the phase modulation value mayinclude information regarding a location from which the reproduced imageis to be projected on a space. Thus, the first hologram pattern PL mayinclude both the information regarding the image that is to bereproduced and the information regarding the location from which thereproduced image is to be projected. The phase modulation value may beestablished to allow the first hologram image L formed by modulating thelight emitted from the illumination unit 110 with the first hologrampattern PL incident to the left eye EL viewing zone of the observer. Forexample, the control unit 130 may calculate the phase modulation valueby determining a and 8 values according to a pupil location of the lefteye EL of the observer, which is provided by the eye tracking unit 150.The control unit 130 may generate the hologram signal by multiplying thephase modulation value and the CGH data of the image and provide thehologram signal to the spatial light modulator 120. The spatial lightmodulator 120 may form the first hologram pattern PL represented as amultiplication of the phase modulation value and the hologram dataaccording to the hologram signal. Then, the first hologram image L maybe formed in the left eye EL viewing zone of the observer according tothe phase modulation value of the first hologram pattern PL.

Referring to FIG. 2B, the spatial light modulator 120 forms a secondhologram pattern PR=HR×tR according to the hologram signal provided bythe control unit 130 at a second time. The illumination unit 110provides the light to the spatial light modulator 120. Then, the lightincident to the spatial light modulator 120 is diffracted and modulatedby the second hologram pattern PR and thus object light may bereproduced. The object light may be projected to a right eye ER viewingzone of the observer, and thus, a second hologram image R may be formed.Thus, the second hologram image R may be seen by the right eye ER of theobserver at the second time.

As described above, to form the second hologram image R in the right eyeER viewing zone of the observer by exactly projecting the object lightto the right eye ER viewing zone of the observer, the phase modulationtransfer function may be used according to Equation 1 above. Forexample, the control unit 130 may calculate a phase modulation value bydetermining a and 8 values according to a pupil location of the righteye ER of the observer, which is provided by the eye tracking unit 150.The control unit 130 may generate a hologram signal by multiplying aphase modulation value and CGH data of an image and provide the hologramsignal to the spatial light modulator 120. The spatial light modulator120 may form the second hologram pattern PR represented as amultiplication of the phase modulation value and the hologram dataaccording to the hologram signal. Then, the second hologram image R maybe formed in the right eye ER viewing zone of the observer according tothe phase modulation value of the second hologram pattern PR.

In a time division method, the spatial light modulator 120 generallyscans the first hologram pattern PL and the second hologram pattern PRalternately in a progressive scan way. For example, FIG. 3 is anexemplary diagram of a process in which the spatial light modulator 120scans the first and second hologram patterns PL and PR in a progressivescan way when alternately forming the first and second hologram images Land R in a time divisional way. Referring to FIG. 3, the spatial lightmodulator 120 may display the first hologram pattern PL in a firstframe, display the second hologram pattern PR in a second frame that issubsequent to the first frame, and display the first hologram pattern PLagain in a third frame that is subsequent to the second frame. The firsthologram pattern PL of the first frame and the second hologram patternPR of the second frame may have different pieces of viewpointinformation regarding a same image. The first hologram pattern PL of thefirst frame and the first hologram pattern PL of the third frame mayhave temporally continuous image information having a same viewpoint.

However, the first and second hologram patterns PL and PR may besimultaneously displayed on the spatial light modulator 120 during atransition period between frames. For example, during a transitionperiod T1 between the first and second frames, the first hologrampattern PL may be partially displayed on a partial region of the spatiallight modulator 120, and the second hologram pattern PR may be partiallydisplayed on a remaining partial region thereof. Likewise, during atransition period T2 between the second and third frames, the secondhologram pattern PR may be partially displayed on a partial region ofthe spatial light modulator 120, and the first hologram pattern PL maybe partially displayed on a remaining partial region thereof.

Thus, if the first hologram pattern PL and the second hologram patternPR have a same phase modulation value, binocular crosstalk, in which thefirst hologram image L is formed in a right eye ER viewing zone of anobserver or the second hologram image R is formed in a left eye ELviewing zone of the observer during the transition periods T1 and T2,may occur. To prevent the binocular crosstalk, the control unit 130 ofthe holographic display apparatus 100 according to an exemplaryembodiment may establish a first phase modulation value tL of the firsthologram pattern PL and a second phase modulation value tR of the secondhologram pattern PR to be different from each other such that hologramimages having different viewpoints reproduced by the first hologrampattern PL and the second hologram pattern PR may be formed on differentspaces.

For example, FIG. 4 is an exemplary diagram of the holographic displayapparatus 100 that provides hologram images L and R of differentviewpoints to left and right-eye viewing zones EL and ER of an observerwithout binocular crosstalk during a transition period between frames.Referring to FIG. 4, the first hologram pattern PL is formed in a lowerarea of the spatial light modulator 120 and the second hologram patternPR is formed in an upper area thereof. The control unit 130 mayestablish the first phase modulation value tL and the second phasemodulation value tR to be different from each other such that the firsthologram image L formed by the first hologram pattern PL travels to theleft eye EL viewing zone of the observer and the second hologram image Rformed by the second hologram pattern PR travels to the left eye ELviewing zone of the observer. Thus, the holographic display apparatus100 may provide the hologram images L and R of different viewpoints tothe left EL and right ER eye viewing zones of the observer withoutbinocular crosstalk during the transition period between frames.

Although the holographic display apparatus 100 may alternately form thefirst hologram image L and the second hologram image R in a timedivisional method as described above, the holographic display apparatus100 may simultaneously form the first hologram image L and the secondhologram image R by overlapping the first hologram pattern PL and thesecond hologram pattern PR according to a hologram characteristic. Forexample, FIG. 5 is an exemplary diagram of the holographic displayapparatus 100 that simultaneously provides the first and second hologramimages L and R of different viewpoints to the left and right-eye viewingzones EL and ER of an observer. Referring to FIG. 5, the spatial lightmodulator 120 displays the first hologram pattern PL=HL×tL and thesecond hologram pattern PR=HR×tR on a frame by overlapping the firsthologram pattern PL=HL×tL and the second hologram pattern PR=HR×tRaccording to a hologram signal provided by the control unit 130.

FIG. 6 is an exemplary diagram for describing a process in which thespatial light modulator 120 scans the first and second hologram patternsPL and PR when simultaneously providing the first and second hologramimages L and R of different viewpoints to the left and right-eye viewingzones EL and ER of an observer. Referring to FIG. 6, the spatial lightmodulator 120 may scan first and second hologram patterns PL1 and PR1overlapping on a first frame, first and second hologram patterns PL2 andPR2 overlapping on a second frame, and first and second hologrampatterns PL3 and PR3 overlapping on a third frame in a progressivescanning method.

Referring to FIG. 5, when the first hologram pattern PL and the secondhologram pattern PR overlap and are displayed on a frame, binocularcrosstalk may be prevented by differently establishing the first phasemodulation value tL of the first hologram pattern PL and the secondphase modulation value tR of the second hologram pattern PR. Forexample, if light emitted by the illumination unit 110 is modulated bythe first hologram pattern PL and the second hologram pattern PRsimultaneously displayed by the spatial light modulator 120, the firsthologram image L and the second hologram image R are respectivelyformed. In this regard, the first phase modulation value tL of the firsthologram pattern PL may be selected such that the first hologram image Lapproaches the left eye EL viewing zone of the observer, and the secondphase modulation value tR of the second hologram pattern PR may beselected such that the second hologram image R approaches the right eyeER viewing zone of the observer. Thus, the first hologram image L andthe second hologram image R may be simultaneously formed withoutcrosstalk.

It has been described that the illumination unit 110 includes one lightsource unit. To form the first hologram image L and the second hologramimage R using one light source unit, the spatial light modulator 120 mayhave a high resolution owing to a very small pixel pitch. However, whenthe illumination unit 110 uses two light source units, the condition ofresolution of the spatial light modulator 120 may be relaxed.

For example, FIG. 7 is a conceptual diagram schematically showing astructure of a holographic display apparatus 200 according to anotherexemplary embodiment. Referring to FIG. 7, the holographic displayapparatus 200 according to an exemplary embodiment may include a spatiallight modulator 120 forming a hologram pattern for modulating light, anillumination unit 110 (e.g., illuminator) providing the light to thespatial light modulator 120, and a control unit 130 (e.g., controller)controlling operations of the spatial light modulator 120 and theillumination unit 110. The holographic display apparatus 100 may furtherinclude an eye tracking unit 150 tracking a pupil location of anobserver.

The illumination unit 110 may include a first light source unit 110L fora hologram image that is to be formed on a left eye EL of the observerand a second light source unit 110R for a hologram image that is to beformed on a right eye ER of the observer. The first and second lightsource units 110L and 110R may be disposed to emit light which isinclined incident to the spatial light modulator 120. For example, thefirst light source unit 110L may be disposed diagonally opposite to theleft eye EL of the observer with respect to a center of the spatiallight modulator 120, and the second light source unit 120L may bedisposed diagonally opposite to the right eye ER of the observer withrespect to the center of the spatial light modulator 120. The first andsecond light source units 110L and 110R may be laser light sources or anarray of LEDs providing light having spatial coherence.

The holographic display apparatus 200 may further include a lens 140allowing a reproduction light formed by modulating light by using thespatial light modulator 120 to be focused on a predetermined space. Thereproduction light is focused on the predetermined space by the lens140, and thus, the hologram image may be formed on the space. The lens140 is disposed between the illumination unit 110 and the spatial lightmodulator 120 in FIG. 7 but is not limited thereto. For example, thelens 140 may be disposed in front of the spatial light modulator 120,e.g., between the spatial light modulator 120 and the observer. If theillumination unit 110 provides a focused beam, the lens 140 may beomitted.

For example, FIGS. 8A and 8B are exemplary diagrams of operations of theholographic display apparatus 200 of FIG. 7 providing hologram imageshaving different viewpoints to the left and right-eye viewing zones ELand ER of an observer in a time divisional way.

Referring to FIG. 8A, the spatial light modulator 120 forms the firsthologram pattern PL according to a hologram signal provided by thecontrol unit 130 at a first time. The first light source unit 110Lprovides light to the spatial light modulator 120 according to thecontrol of the control unit 130. Then, the light from the first lightsource unit 110L is diffracted and modulated by the first hologrampattern PL, and thus, object light may be reproduced. The object lightmay be projected to the left eye EL viewing zone of the observer, andthus, the first hologram image L may be formed. Thus, the first hologramimage L may be seen by the left eye EL of the observer at the firsttime.

As described above, to form the first hologram image L in the left eyeEL viewing zone of the observer by exactly projecting the object lightto the left eye EL viewing zone of the observer, a phase modulationtransfer function such as Equation 1 may be used. That is, the firsthologram pattern PL may be expressed as a multiplication HL×tL of thephase modulation value tL of the phase modulation transfer function ofEquation 1 above and the hologram data HL of the first hologram image L.The phase modulation value may be established to allow the firsthologram image L formed by modulating the light emitted from the firstlight source unit 110L with the first hologram pattern PL incident tothe left eye EL viewing zone of the observer.

Referring to FIG. 8B, the spatial light modulator 120 forms the secondhologram pattern PR=HR×tR according to the hologram signal provided bythe control unit 130 at a second time. The second light source unit 110Rprovides light to the spatial light modulator 120 according to thecontrol of the control unit 130. Then, the light is diffracted andmodulated by the second hologram pattern PR and thus object light may bereproduced. The object light may be projected to the right eye ERviewing zone of the observer, and thus, the second hologram image R maybe formed. Thus, the second hologram image R may be seen by the righteye ER of the observer at the second time.

In this regard, to form the second hologram image R in the right eye ERviewing zone of the observer by exactly projecting the object light tothe right eye ER viewing zone of the observer, the phase modulationtransfer function may be used according to Equation 1 above. That is,the second hologram pattern PR may be expressed as a multiplicationHR×tR of the phase modulation value tR of the phase modulation transferfunction of Equation 1 above and the hologram data HR of the secondhologram image R. The phase modulation value may be established to allowthe second hologram image R formed by modulating the light emitted fromthe second light source unit 110R with the second hologram pattern PRincident to the right eye ER viewing zone of the observer.

However, as shown with reference to FIG. 3 above, if the spatial lightmodulator 120 scans the first hologram pattern PL and the secondhologram pattern PR alternately in a progressive scan method, the twohologram patterns PL and PR may be simultaneously displayed on thespatial light modulator 120 during a transition period between frames.Thus, if the first hologram pattern PL and the second hologram patternPR have a same phase modulation value, binocular crosstalk, in which thefirst hologram image L is formed in a right eye ER viewing zone of anobserver or the second hologram image R is formed in a left eye ELviewing zone of the observer during the transition periods T1 and T2,may occur. For example, if the second light source unit 110R provideslight to the spatial light modulator 120, as shown in FIG. 8B, duringthe transition period T1 between the first and second frames, imageshaving different viewpoints formed by the second hologram pattern PR andthe first hologram pattern PL displayed on the spatial light modulator120 may be formed in the right eye ER viewing zone of the observer. Ifthe first light source unit 110L provides light to the spatial lightmodulator 120, as shown in FIG. 8A, during the transition period T2between the second and third frames, images having different viewpointsformed by the first hologram pattern PL and the second hologram patternPR displayed on the spatial light modulator 120 may be formed in theleft eye EL viewing zone of the observer.

To prevent the binocular crosstalk, the control unit 130 of theholographic display apparatus 200 according to an exemplary embodimentmay establish the first phase modulation value tL of the first hologrampattern PL and the second phase modulation value tR of the secondhologram pattern PR to be different from each other such that hologramimages having different viewpoints formed by the first hologram patternPL and the second hologram pattern PR may be formed on different spaces.For example, FIG. 9A is an exemplary diagram of an operation of theholographic display apparatus 200 generating a hologram image in theright eye ER viewing zone of an observer when the second light sourceunit 110R provides light to the spatial light modulator 120, and FIG. 9Bis an exemplary diagram of an operation of the holographic displayapparatus 200 generating a hologram image in the left eye EL viewingzone of an observer when the first light source unit 110L providesincident light to the spatial light modulator 120.

Referring to FIG. 9A, during the transition period T1 between first andsecond frames, the second light source unit 110R provides light to thespatial light modulator 120. The second hologram pattern PR may bepartially displayed on a partial region of the spatial light modulator120, and the first hologram pattern PL may be partially displayed on aremaining partial region thereof. Then, the light emitted by the secondlight source unit 110R is incident on both the second hologram patternPR and the first hologram pattern PL. Thus, the light emitted by thesecond light source unit 110R is modulated by the second hologrampattern PR and the first hologram pattern PL so that second and thirdhologram images R and L′ having different viewpoints are formed. Thesecond hologram image R is a normal image, whereas the third hologramimage L′ is an abnormal image that causes crosstalk in the right eye ERviewing zone of the observer. The control unit 130 establishes thesecond phase modulation value tR of the second hologram pattern PR suchthat the normal second hologram image R may be exactly incident to theright eye ER viewing zone. To prevent the crosstalk, the control unit130 establishes the first phase modulation value tL of the firsthologram pattern PL such that the third hologram image L′ may beincident to a location beyond the right eye ER viewing zone of theobserver. Then, as shown in FIG. 9A, only the second hologram image R isincident on the right eye ER viewing zone of the observer, therebypreventing the crosstalk.

Referring to FIG. 9B, during the transition period T2 between second andthird frames, the first light source unit 110L provides light to thespatial light modulator 120. The first hologram pattern PL may bepartially displayed on a partial region of the spatial light modulator120, and the second hologram pattern PR may be partially displayed on aremaining partial region thereof. Then, the light emitted by the firstlight source unit 110L is incident on both the first hologram pattern PLand the second hologram pattern PR. Thus, the light emitted by the firstlight source unit 110L is modulated by the first hologram pattern PL andthe second hologram pattern PR so that first and fourth hologram imagesL and R′ having different viewpoints are formed. The first hologramimage L is a normal image, whereas the fourth hologram image R′ is anabnormal image that causes crosstalk in the left eye EL viewing zone ofthe observer. The control unit 130 establishes the first phasemodulation value tL of the first hologram pattern PL such that thenormal first hologram image L may be exactly incident to the left eye ELviewing zone. To prevent the crosstalk, the control unit 130 establishesthe second phase modulation value tR of the second hologram pattern PRsuch that the fourth hologram image R′ may be incident to a locationbeyond the left eye EL viewing zone of the observer. Then, as shown inFIG. 9B, only the first hologram image L is incident on the left eye ELviewing zone of the observer, thereby preventing the crosstalk.

In conclusion, the first phase modulation value tL may be establishedsuch that the normal first hologram image L formed by modulating thelight emitted by the first light source unit 110L by using the firsthologram pattern PL may be incident on the left eye EL viewing zone ofthe observer, and the abnormal third hologram image L′ formed bymodulating the light emitted by the second light source unit 110R byusing the first hologram pattern PL may be incident on the locationbeyond the right eye ER viewing zone of the observer. The second phasemodulation value tR may be established such that the normal secondhologram image R formed by modulating the light emitted by the secondlight source unit 110R by using the second hologram pattern PR may beincident to the right eye ER viewing zone of the observer, and theabnormal fourth hologram image R′ formed by modulating the light emittedby the first light source unit 110L by using the second hologram patternPR may be incident on the location beyond the left eye EL viewing zoneof the observer. The first hologram pattern PL may be represented as amultiplication HL×tL of the hologram data HL of the first hologram imageL and the first phase modulation value tL, and the second hologrampattern PR may be represented as a multiplication HR×tR of the hologramdata HR of the second hologram image R and the second phase modulationvalue tR.

As shown in FIG. 10, the observer may recognize the normal firsthologram image L and second hologram image R that are incident on thepupils of the left eye EL and the right eye ER of the observer, whereasthe observer may not recognize the abnormal third hologram image L′ andthe fourth hologram image R′ that are beyond the pupils of the left eyeEL and the right eye ER of the observer, thereby preventing thecrosstalk.

As described above, no crosstalk occurs by the fourth hologram image R′formed by modulating the light emitted by the first light source unit110L by using the second hologram pattern PR and the third hologramimage L′ formed by modulating the light emitted by the second lightsource unit 110R by using the first hologram pattern PL, and thus, it isunnecessary to alternately emit light by the first light source unit110L and the second light source unit 110R. For example, FIG. 11 is anexemplary diagram of an operation of the holographic display apparatus200 generating the hologram images L and R in left eye EL and right eyeER viewing zones of an observer when the first and second light sourceunits 110L and 110R provide light to the spatial light modulator 120.FIG. 12 is an exemplary timing diagram of a process of operating theillumination unit 110 and the spatial light modulator 120 in theoperation of the holographic display apparatus 200 of FIG. 11

As shown in FIGS. 11 and 12, although both of the first and second lightsource units 110L and 110R provide the light to the spatial lightmodulator 120, the observer may recognize the normal first and secondhologram images L and R that are exactly incident on the pupils of theleft eye EL and the right eye ER of the observer, whereas the observermay not recognize the abnormal third hologram image L′ that is beyondthe pupils of the right eye ER of the observer. The observer may notalso recognize the abnormal fourth hologram image R′ that is beyond thepupils of the left eye EL of the observer.

Therefore, it is unnecessary to alternately operate the first and secondlight source units 110R and 110L in synchronization with a frame periodof the spatial light modulator 120, and thus, a configuration of theholographic display apparatus 200 may be simplified. According to anexemplary embodiment, when the first and second hologram images L and Rare provided in a time divisional way, since there is no need to insertan intermediate frame for preventing crosstalk between a frame of thefirst hologram image L and a frame of the second hologram image R, animage frame rate of the holographic display apparatus 200 may beimproved.

When locations of the pupils are changed when the eyes of the observermove, the control unit 130 may change first and second phase modulationvalues with respect to a pupil location change of the observer based oninformation provided by the eye tracking unit 150. The control unit 130may reestablish the first and second phase modulation values so as toprevent the crosstalk even when the first and second phase modulationvalues are changed according to the pupil location change of theobserver. For example, the control unit 130 may change the first andsecond phase modulation values such that a location difference betweenthe first hologram image L and the fourth hologram image R′ and alocation difference between the second hologram image R and the thirdhologram image L′ may be maintained to be greater than sizes of thepupils of the observer in response to the pupil location change of theobserver.

FIGS. 13A, 13B, 14A, and 14B are actually formed hologram images inwhich no crosstalk occurs. FIGS. 13A, 13B, 14A, and 14B show results ofcapturing hologram images by actually forming the hologram image andplacing cameras in left eye EL and right eye ER viewing zones, to showthat the crosstalk may be removed by using the above-described method.In more detail, FIG. 13A is a result of photographing the first hologramimage L having a depth of +100 mm by using a camera in the left eye ELviewing zone, and FIG. 13B is a result of capturing the second hologramimage R having the depth of +100 mm by using a camera in the right eyeER viewing zone. FIG. 14A is a result of capturing the second hologramimage R having a depth of 0 mm by using the camera in the right eye ERviewing zone, and FIG. 14B is a result of capturing the second hologramimage R having the depth of 0 mm by using the camera in the left eye ELviewing zone. As shown in FIGS. 13A, 13B, 14A, and 14B, no crosstalkoccurs in the images captured by using the cameras in the left eye ELviewing zone and the right eye ER viewing zone.

Although a holographic display method of alternately forming the firsthologram image L and the second hologram image R in a time divisionalway is described above, the first hologram image L and the secondhologram image R may be simultaneously formed by overlapping the firsthologram pattern PL and the second hologram pattern PR according to ahologram characteristic. FIG. 15 is an exemplary diagram of an operationof the holographic display apparatus 100 simultaneously providing thefirst and second hologram images L and R having different viewpoints ina left eye EL viewing zone and a right eye ER viewing zone of anobserver. FIG. 16 is an exemplary timing diagram of a process ofoperating the illumination unit 110 and the spatial light modulator 120in the operation of the holographic display apparatus 200 of FIG. 15.Referring to FIGS. 15 and 16, the spatial light modulator 120 displaysthe first hologram pattern PL and the second hologram pattern PR on aframe by overlapping the first hologram pattern PL and the secondhologram pattern PR according to a hologram signal provided by thecontrol unit 130.

For example, as shown in FIG. 16, the spatial light modulator 120 mayscan first and second hologram patterns PL1 and PR1 overlapping on afirst frame, first and second hologram patterns PL2 and PR2 overlappingon a second frame, and first and second hologram patterns PL3 and PR3overlapping on a third frame in a progressive scanning way.

Referring to FIG. 15, when the first hologram pattern PL and the secondhologram pattern PR overlap and are displayed on a frame, binocularcrosstalk may be prevented by establishing a first phase modulationvalue of the first hologram pattern PL and a second phase modulationvalue of the second hologram pattern PR to be different from each other.For example, if light emitted by the first light source unit 110L ismodulated by the first hologram pattern PL and the second hologrampattern PR simultaneously displayed by the spatial light modulator 120,the first hologram image L and the fourth hologram image R′ arerespectively formed. The first phase modulation value tL of the firsthologram pattern PL may be selected such that the first hologram image Lapproaches the left eye EL viewing zone of the observer, and the secondphase modulation value tR of the second hologram pattern PR may beselected such that the fourth hologram image R′ is beyond the left eyeEL viewing zone of the observer. If light emitted by the second lightsource unit 110R is modulated by the first hologram pattern PL and thesecond hologram pattern PR simultaneously displayed by the spatial lightmodulator 120, the third hologram image L′ and the second hologram imageR are respectively formed. The first phase modulation value tL of thefirst hologram pattern PL may be selected such that the third hologramimage L′ is beyond the right eye ER viewing zone of the observer, andthe second phase modulation value tR of the second hologram pattern PRmay be selected such that the second hologram image R approaches theright eye ER viewing zone of the observer. Thus, the first hologramimage L and the second hologram image R may be simultaneously formedwithout crosstalk.

In the above-described exemplary embodiments, the control unit 130 mayprevent the crosstalk by establishing the first phase modulation valuetL of the first hologram pattern PL and the second phase modulationvalue tR of the second hologram pattern PR. As described above, thecontrol unit 130 may be implemented by using software or a semiconductorchip functioning as the software, and thus, no additional machine orelectronic device may be required to prevent the crosstalk.

Cases where each of the holographic display apparatuses 100 and 200forms the two hologram images L and R of different viewpoints in twoviewing zones of different spatial locations are described above.However, the exemplary embodiments are not limited thereto, andaccording to other exemplary embodiments, three or more hologram imagesof different viewpoints may be formed in three or more viewing zones.For example, the spatial light modulator 120 may form three or morehologram patterns sequentially or simultaneously by overlapping thethree or more hologram patterns, and the control unit 130 may establishphase modulation values of the three or more hologram patterns to bedifferent from each other. In this regard, the control unit mayestablish the phase modulation values such that gaps between three ormore different viewing zones are maintained to be greater than sizes ofthe pupils of an observer. For example, the control unit may establish aphase modulation value of each of three or more hologram patterns suchthat location differences between three or more hologram images ofdifferent viewpoints reproduced by the three or more hologram patternsare maintained to be greater than the sizes of the pupils of theobserver.

To facilitate understanding of the exemplary embodiments, holographicdisplay apparatuses and holographic display methods according to certainexemplary embodiments have been described and shown in the accompanyingdrawings. However, it should be understood that such exemplaryembodiments are merely intended to illustrate the exemplary embodimentsand not to limit the exemplary embodiments. It should be also understoodthat the exemplary embodiments are not limited to the illustrated andprovided description. This is because various modifications may be madeby those of ordinary skill in the art.

What is claimed is:
 1. A holographic display apparatus comprising: aspatial light modulator configured to generate hologram patterns tomodulate light; and an illuminator configured to emit the light to thespatial light modulator, wherein the spatial light modulator isconfigured to generate, from among the hologram patterns, a firsthologram pattern and a second hologram pattern according to controloperations of the holographic display apparatus, the first hologrampattern and the second hologram pattern being configured to form a firsthologram image and a second hologram image having different viewpoints,and wherein the holographic display apparatus is configured to set afirst phase modulation value of the first hologram pattern and a secondphase modulation value of the second hologram pattern to be differentfrom each other such that hologram images having different viewpointsformed by the first hologram pattern and the second hologram pattern areformed on different spatial locations, and wherein the holographicdisplay apparatus is configured to control the spatial light modulatorto alternately scan the first hologram pattern and the second hologrampattern in a progressive scanning way in order to alternately form thefirst hologram image and the second hologram image in a time divisionway.
 2. The holographic display apparatus of claim 1, wherein thespatial light modulator is configured to display the first hologrampattern on a first frame, the second hologram pattern on a second framethat is subsequent to the first frame, a part of the first hologrampattern on a partial area of the spatial light modulator, and a part ofthe second hologram pattern on a remaining partial area of the spatiallight modulator during a transition period between the first frame andthe second frame.
 3. The holographic display apparatus of claim 2,wherein the holographic display apparatus is configured to set the firstphase modulation value such that the first hologram image modulated andformed by the first hologram pattern is transmitted to a first viewingzone and to set the second phase modulation value such that the secondhologram image modulated and formed by the second hologram pattern istransmitted to a second viewing zone different from the first viewingzone during the transition period.
 4. The holographic display apparatusof claim 1, wherein the illuminator comprises one light sourceconfigured to emit light.
 5. The holographic display apparatus of claim4, wherein the holographic display apparatus is configured to set thefirst phase modulation value such that the first hologram image formedby modulating light emitted by the light source by using the firsthologram pattern is incident to a first viewing zone, and to set thesecond phase modulation value such that the second hologram image formedby modulating the light emitted by the light source by using the secondhologram pattern is incident to a second viewing zone different from thefirst viewing zone.
 6. The holographic display apparatus of claim 1,wherein the illuminator comprises a first light source configured toemit light for forming the first hologram image and a second lightsource configured to emit light for forming the second hologram image.7. The holographic display apparatus of claim 6, wherein the holographicdisplay apparatus is configured to set the first phase modulation valuesuch that the first hologram image formed by modulating light emitted bythe first light source by using a first hologram pattern is incident toa first viewing zone, and a third hologram image formed by modulatinglight emitted by the second light source by using the first hologrampattern is incident to a location beyond a second viewing zone.
 8. Theholographic display apparatus of claim 7, wherein the holographicdisplay apparatus is configured to set the second phase modulation valuesuch that the second hologram image formed by modulating the lightemitted by the second light source by using a second hologram pattern isincident to the second viewing zone, and a fourth hologram image formedby modulating the light emitted by the first light source by using thesecond hologram pattern is incident to a location beyond the firstviewing zone.
 9. The holographic display apparatus of claim 8, furthercomprising: an eye tracker configured to track a pupil location of anobserver observing the first hologram image, the second hologram image,the third hologram image and the fourth hologram image, wherein theholographic display apparatus is configured to change the first phasemodulation value and the second phase modulation value such that alocation difference between the first hologram image and the fourthhologram image and a location difference between the second hologramimage and the third hologram image are maintained to be greater thansizes of pupils of the observer in response to a pupil location changeof the observer.
 10. The holographic display apparatus of claim 6,wherein the first light source and the second light source areconfigured to simultaneously provide light to the spatial lightmodulator.
 11. The holographic display apparatus of claim 1, wherein thefirst hologram pattern is represented as a product of hologram data ofthe first hologram image multiplied with the first phase modulationvalue, and the second hologram pattern is represented as a product ofhologram data of the second hologram image multiplied with the secondphase modulation value.